Selenium rectifier



NW, 15, 1949 w. E. BLACKBURN &

SELENIUM RECTIFIER Filed Dec. 15, 1943 C 07 jfiaamz'wrz 12 i 4 a 277/0222 z// 7720? m 3 SZQEZ WITNESSES: INVENTOR Wayne 5. Blue/{warn ATTORNEY Patented Nov. 15, 1949 SELENIUM RECTIFIER Wayne E. Blackburn, Wilkinsburg, Pa... assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 15, 1943, Serial No. 514,371

9 Claims. (Cl. 175-3.66)

My invention relates to dry-contact rectifiers or light-sensitive devices and particularly to devices of this type which employ a layer of selenium.

One object of my invention is to provide a selenium rectifier or light-sensitive device in which the surface of the selenium at which the rectification or photo-electric effect is produced is provided with a boundary layer which insures a high resistance to current flow in the nominally non-conductive direction when an alternating voltage is impressed upon it. Such a layer may be referred to as a blocking layer.

Another object of my invention is to produce on a selenium layer a blocking layer which has a high resistance to current flow in the nominally non-conductive direction but which does not introduce a high resistance to current flow in the nominally conductive direction.

Another object of my invention is to provide a selenium layer with a blocking layer which shall not undergo such chemical reaction during the practical use of the device incorporating it that the latter will change its electrical characteristics, or as it is sometimes termed will age, at a deleterious rate in service.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawing in which, Fig. 1 is an elevation and Fig. 2 a top view of a rectifier embodying the principles ofmy invention.

Referring in details to the drawing the rectifier comprises a base-plate I which may comprise steel which has first been sand-blasted on the surface and thereafter nickel-plated. The plate I thus prepared is preferably provided with a central hole 2 by which it may be mounted upon a spindle provided with means for rapidly rotating it. The plate and spindle while in rotation are dipped into molten selenium and then withdrawn therefrom. The centrifugal force removes all of the selenium except a thin uniform layer 3 from the surface of the plate. The surface of the selenium is coated by evaporation and condensation with cadmium sulphide 4. The coating process may be carried out by heating cadmium sulphide inside an enclosure which is preferably evacuated to a pressure below about /40 of atmospheric. While the unit thus produced may tin. I prefer in accordance with the process described in my copending application Serial No. 509,817, filed November 10, 1943, now Patent No. 2,447,630, to apply the said contact layer first to the cadmium sulphide surface and thereafter to anneal the unit by heating it to the temperature of the order of C. for a suitable period, for example, for a time between six and sixteen hours. The unit rectifier, when made in accordance with the process just described, may then be connected to electrical circuits in any of the standard connections for rectifier discs.

While I have described the application to the surface of the selenium as comprising cadmium sulphide, other metallic compounds of the sulphur family may be substituted therefor; for example, mercuric sulphide or potassium sulphide may be substituted.

I claim as my invention:

1. The method of forming a blocking layer on selenium which comprises producing thereon a layer of cadmium sulphide.

2. The method of producing an electric circuit element embodying selenium which comprises forming a surface of selenium and superposing thereon a layer of cadmium sulphide.

3. The method of producing ari electrical circuit element which comprises depositing by evaporation on a surface of amorphous selenium a layer of cadmium sulphide.

4. The method of making a selenium rectifier which comprises coating a base-plate with selenium, depositing a layer of cadmium sulphide by evaporation on the free surface of the selenium producing a contact layer on the free surface of the cadmium sulphide and heating the resultant unit to a temperature of the order of 185 C.

5. The method of making a selenium rectifier which comprises coating a base-plate with selenium, depositing a. layer of cadmium sulphide by evaporation on the free surface of the selenium, producing a contact layer on the free surface of the cadmium sulphide and heating the resultant unit to a temperature of the order of 185 C. for a period of at least six hours.

6. An-electrical circuit element comprising a 4 being coated at least in part with a layer'oi' m mm) cadmium.

8. A rectifier comprising a base-plate having The following references are of record in the a coating of selenium with a coating oftgzdmium file of this patent: sulphide on its free surface and a con t layer .on the free surface of the cadmium sulphide. 5 UNITED STATES PATENTS 9. .A rectifier comprising a base-plate having Number Name Date a layer of selenium which has a coating of 2,121,603 Lotz June 21, 1938 cadmium sulphide on its free surface, the free 2,193,610 Wilson Mar. 12, 1940 surface of the cadmium sulphide being coated m 2,195,725 Hoppe Apr. 2, 1940 with cadmium. 1 2,221,596 Lorenz Nov. 12, 1940 2,227,827 Dubar Jan. 7, 1941 WAYNE E. BLACKBURN. 2,279,187 Thompson Apr. 7, 1942 

